1. Field of the Invention
This invention relates in general to turbochargers and, more particularly, to a turbocharger having a pressure-gain combustor placed downstream of the turbine.
2. Description of the Prior Art
Turbocharging is a widely accepted method for increasing the power output, torque, and specific power output of an internal combustion engine. One of the key criteria in designing a turbocharged engine is that the characteristics of the turbocharger be properly matched to the compressor and all of the engine components. However, because it is impossible for the operating conditions of the compressor, turbine, and i.c. engine to be identical at all load ratings, most designers match the components at the higher load rating, which inevitably compromises performance at no-load or partial load conditions. This results in the problem known as "turbo lag", wherein the power of the engine is reduced during start-up and other low speed conditions. As a result of increased start-up torque requirements, the problem of turbo lag becomes more severe for higher design point charge pressure.
One solution to turbo lag which has been proposed in the past has been to provide the turbine assembly with multiple vanes which function like adjustable louvers. The adjustable vanes enable an operator to vary the turbine flow area, and hence, the exhaust velocity past the turbine wheel, thus controlling the turbocharger speed and boost level. A major problem with this approach, however, is that the adjustable louvers increase the overall complexity and manufacturing cost of the engine, making it impractical for all but a few applications.
Another solution has been to make the rotor out of lightweight ceramic material, which reduces the rotor's polar moment of inertia. This enables the rotor to accelerate faster, which in turn leads allows the turbocharger to reach its maximum boost level sooner. A drawback ceramic rotors has been their increased fragility, since any particle drawn into the turbocharger exhaust could potentially damage the rotor. Recently, an attempt to reduce this risk has been made by providing the turbine housing with an integral particle trap which removes exhaust particles before they reach the rotor. Once again, however, this approach leads to increased cost and complexity which in many cases outweighs the benefits of improved boost.
Accordingly, a need exists for a new and improved device for boosting the power of a turbocharged engine in a simple and cost-effective manner.